As a steering apparatus of this type, there is known an attaching construction of a steering column lower joint portion in which a fastening bolt is brought into engagement with a cut-out groove which is formed on a connecting shaft portion of a steering column which is connected to a connecting shaft portion of a steering gear part via a lower joint, so as to fix a top lower joint by tightening the bolt and the fastening bolt is brought into engagement with a cut-out recess portion which is formed on the connecting shaft portion, so as to fix a bottom lower joint to the connecting shaft portion by tightening the bolt, wherein a temporary fastening stepped groove portion is provided in such a manner as to extend from the cut-out groove, and a small diameter portion adapted to be brought into engagement with the temporary fastening stepped groove portion so as to temporarily fasten the top lower joint to the connecting shaft portion and a large diameter portion adapted to be brought into engagement with the cut-out groove so as to finally fix the top lower joint to the connecting portion are formed on the fastening bolt (for example, JP-UM-A-06-72780, page 1, FIG. 9).
As is shown in FIG. 49, in a steering apparatus for imparting a steering angle to steered road wheels, a steering shaft 102 having a steering wheel 101 fixed to a rear end portion thereof is supported rotatably on an inside diameter side of a steering column 103 which is supported on a vehicle body. In addition, a rear end portion of an intermediate shaft 105 is connected to a front end portion of the steering shaft 102 via a universal joint 104, and a rear end portion of an input shaft 108 of a steering gear unit 107 is connected to a front end portion of the intermediate shaft 105 via a universal joint 106. When the driver operates to turn the steering wheel 101 in this state, the rotational force is transmitted to the steering gear unit 107 via the aforesaid respective members 102, 104, 105, 106. As a result of this, tie rods (not shown) connected to both end portions in an axial direction (in a front-back direction of FIG. 49) of the steering gear unit 107 are pushed and pulled to thereby impart a steering angle to the left and right steered road wheels (not shown).
FIG. 50 shows a connecting portion between a shaft and a yoke of a universal joint that is described in JP-A-2000-249157 as a conventional construction of such a connecting portion. FIG. 50 is an exploded perspective view of a connecting portion between the front end portion of the aforesaid intermediate shaft 105 and one yoke 109 which makes up the aforesaid universal joint 106. A segmental cylindrical tube-shaped shaft attaching portion 110 is provided at a base half portion (a right-hand upper half portion of FIG. 50) of the one yoke 109. In addition, an inner circumferential surface of this shaft attaching portion 110 is made into a female serration portion 111. Additionally, a pair of flange portions 112a, 112b which are parallel to each other are provided at both edges in a circumferential direction of the shaft attaching portion 110. In addition, of the pair of flange portions, a through hole 113 is formed in part of one flange portion 112a, while a thread hole (not shown) is formed in part of the other flange portion 112b, the through hole 113 and the tread hole being formed coaxially with each other. On the other hand, an outer circumferential surface of the front end portion of the intermediate shaft 105 is made into a male serration portion 114. In addition, an engagement projecting portion 115 is formed at one location in the circumferential direction along a front edge on the outer circumferential surface of the intermediate shaft 105. This engagement projecting portion 115 is formed by plastically deforming the material of the intermediate shaft 105 at portions which lie circumferentially on both sides of a portion where the engagement projecting portion 115 is to be formed and drawing the material centrally to the portion so that the material so drawn is caused to rise radially outwards.
When connecting the front end portion of the intermediate shaft 105 and the one yoke 109 together, prior to the connection of the front end portion and the yoke, the universal joint 106 is fabricated in advance by connecting a bifurcated distal end portion of the one yoke 109 (a left-hand lower end portion of FIG. 50) and a bifurcated distal end portion of the other yoke 120 together via a cross joint (refer to FIG. 49). Then, in this state, firstly, the front end portion of the intermediate shaft 105 is inserted into an inside of the shaft attaching portion 110, so that the male serration portion 114 is brought into loose serration engagement with the female serration portion 111 (in such a manner as to permit an axial relative displacement). At the same time as this occurs, the engagement projecting portion 115 is caused to enter between both the circumferential edges of the shaft attaching portion 110 (both the flange portions 112a, 112b). In addition, in this state, the engagement projecting portion 115 is made to be disposed axially deeper into the shaft attaching portion 110 (a deeper side in a direction in which the front end portion of the intermediate shaft 105 is inserted, a left-hand lower side of FIG. 50) than the through hole 113 and the thread hole which are formed in both the flange portions 112a, 112b, respectively. Following this, a shank portion 117 of a bolt 116 is inserted into the through hole 113. Further, a male thread portion 118 provided on a distal half portion of the shank portion 117 is screwed into the thread hole, and this bolt 116 is tightened in such a state that a head portion 119 of the bolt 116 is kept in abutment with an outer surface of the one flange portion 112a. By this action, a space between both the flange portions 112a, 112b is narrowed so as to contract the shaft attaching portion 110 in diameter, whereby the female serration portion 111 and the made serration portion 114 are brought into strong serration engagement with each other. As a result of this, the front end portion of the intermediate shaft 105 and the one yoke 109 are connected and fixed to each other.
In addition, as in the case of the steering apparatus shown in FIG. 49, when a construction is adopted in which the other yoke 120 is fixedly welded to an upper end portion of the input shaft 108, the connecting work between the front end portion of the intermediate shaft 105 and the one yoke 109 is performed in such a state that the other yoke 120 is fixedly welded to the upper end portion of the input shaft 108. In contrast to this, when as the other yoke 120, something that can be connected to the upper end portion of the input shaft 108 with a bolt (a so-called side-insertion-type yoke or the like) is adopted, the connecting work between the front end portion of the intermediate shaft 105 and the one yoke 109 can be performed before the other yoke 120 is connected to the upper end portion of the input shaft 108. As this occurs, when the work of connecting the other yoke 120 to the upper end portion of the input shaft 108 is performed after the connection of the front end portion of the intermediate shaft 105 and the one yoke 109, the connecting portion between the front end portion of the intermediate shaft 105 and the one yoke 109 is left in a temporarily fastened state, that is, the bolt 116 is kept in a loosened state only with the male thread portion 118 of the bolt 116 which has been inserted into the through hole 113 being screwed into the thread hole. In this temporarily fastened state, since the female serration portion 111 and the male serration portion 114 are put in a state where they are in loose serration engagement with each other, the front end portion of the intermediate shaft 105 and the one yoke 109 can be displaced relative to each other by a predetermined amount only in an axial direction. Specifically, the axial relative displacement is permitted between a position where the shank portion 117 of the bolt 116 and the engagement projecting portion 115 are brought into engagement with each other and a position where the cross joint 121 and a front end face of the intermediate shaft 105 are brought into abutment with each other. Consequently, the working properties in connecting the other yoke 120 to the upper end portion of the input shaft 108 can be made better by such an extent that such an axial relative displacement is allowed.
In any case, in the case of the connecting portion between the front end portion of the intermediate shaft 105 and the one yoke 109, not only when the work of connecting the other yoke 120 to the upper end portion of the input shaft 108 is performed but also even in case the temporarily fastened state occurs as a result of the bolt 116 getting loosened while a motor vehicle is running, the engagement projecting portion 115 is brought into engagement with the shank portion 117 of the bolt 116, whereby the front end portion of the intermediate shaft 105 can be prevented from being dislocated from the inside of the shaft attaching portion 110 of the one yoke 109 towards a proximal end side thereof.
Incidentally, in the case of the conventional construction that has been described above, a width dimension W of the engagement projecting portion 115 does not have to equal a space D between both the circumferential edges (both the flange portions 112a, 112b) of the shaft attaching portion in such a state that the front end portion of the intermediate shaft 105 is fixedly connected with the one yoke 109. However, from the viewpoint of increasing the accuracy with which the front end portion of the intermediate shaft 105 and the one yoke 109 match in phase with respect to the circumferential direction, the width dimension W is preferably made as close to the space D as possible. In the case of the conventional construction, however, in the event that a yoke in which the space D is wide is adopted as the one yoke 109, it becomes difficult that the width dimension W of the engagement projecting portion 115 is increased so as to match the increased width dimension. This is because as the width dimension W of the engagement projecting portion 115 which is determined in the design stage is made larger, the amount of the material of the intermediate shaft 105 at portions which lie circumferentially on both sides of a portion where the engagement projecting portion 115 is to be formed (the material which is to make up the engagement projecting portion 115) is reduced, easily calling for a shortage of the material. In addition, as another reason, this is because the increasing rate of working force exerted on the engagement projecting portion 115 becomes very large as the width dimension W of the engagement projecting portion 115 is increased and there exists a possibility that a deformation which is not preferred is produced at portions surrounding the worked portion by virtue of the working force so increased.
However, in the conventional example described in JP-UM-A-06-72780, when connecting the steering column shaft and the steering gear part are connected together by the lower joint, the cut-out groove is formed at a lower joint side end portion of the steering column shaft in a position lying in the vicinity of the end face. Further, since the temporary fastening stepped groove portion is made to be formed consecutively to a side of the cut-out groove which is opposite to the end face, in the case of an electric power steering apparatus being equipped on the vehicle as seen on recent vehicles in which a steering assist force is produced by an electric motor so as to be transmitted to a steering column shaft via a reduction gear mechanism, there still exists an unsolved problem that a torque that is to be transmitted to the steering column shaft becomes large and the rigidity of the steering column shaft is reduced due to the cross sectional area of the steering column shaft being reduced by the cut-out groove and the temporary fastening stepped groove portion.
Although it is considered that the depth of the cut-out groove, which configures a weakest portion, is made less deep in order to suppress the reduction in rigidity of the steering column shaft, as this actually occurs, the engagement force between the cut-out groove and the fastening bolt becomes small, and this produces a new problem that no sufficient stopper function can be exhibited when an impact force is transmitted to the steering column shaft in a direction in which the shaft is contracted.